Hydrogenated diels-alder adducts and lactone compounds

ABSTRACT

A hydrogenated Diels-Alder adduct of the formula (III) 
     
       
         
         
             
             
         
       
     
     a hydrogenated Diels-Alder adduct of the formula (IV) 
     
       
         
         
             
             
         
       
     
     and
 
a lactone compound of formula (V)
 
     
       
         
         
             
             
         
       
     
     are disclosed and described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.15/536,708, filed Jun. 16, 2017, which is the U.S. National Stage ofInternational Application No. PCT/NL2015/050882 filed Dec. 18, 2015,which claims the benefit of Netherlands Application No. NL 2014023,filed Dec. 19, 2014, the contents of which is incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to an improved process for the preparationof a benzene compound, more in particular to a process for thepreparation of a benzene compound which comprises a process step whereina furan compound is reacted with an olefin. The reaction of the furancompound with the olefin may be a Diels-Alder reaction.

BACKGROUND OF THE INVENTION

Such a process is known from e.g. WO 2013/048248. In this application itis described that there is an increasing tendency to create chemicalsfrom renewable sources. Research has been undertaken to preparechemicals from biomass materials, such as carbohydrates, e.g. cellulose,starch, hemicelluloses, sugars, glucose and fructose. Dehydration ofsuch carbohydrates may yield valuable chemicals, including levulinicacid, furfural, hydroxymethyl furfural and derivatives thereof. In WO2013/048248 the reaction is disclosed wherein a 2-alkoxymethyl furan isreacted with a substituted olefin to yield an unsaturated bicyclicether. The bicyclic ether is subsequently dehydrated and aromatized toyield a substituted benzene compound. Via this process substituents onthe 1,2-, 1,3- or 1,2,3-positions of the benzene ring are obtained. Thethus obtained products may elegantly be converted by oxidation intophthalic acid, isophthalic acid and hemimellitic acid.

In US 2010/0127220 a process for the manufacture of substitutedpentacenes is described. The process includes a step whereindimethylfuran is reacted with maleic anhydride via a Diels Alderreaction to yield a bicyclic unsaturated ether. The bicyclic unsaturatedether is then dehydrated and aromatized under aromatization conditionsto yield 4,7-dimethyl-isobenzofuran-1,3-dione (see reaction scheme A,wherein step (i) is a Diels-Alder reaction and step (ii) is thearomatization).

It appears that the yield of the bicyclic unsaturated ether can berelatively high. An example in WO 2013/048248 shows that the yield ofthe bicyclic unsaturated ether can be about 96%. According to an examplein US 2010/0127220 a yield of about 72% could be obtained in thepreparation of the bicyclic unsaturated ether (cf. US 2010/0127220,Example 1). However, both documents also show that the yield of thesubsequent dehydration is significantly lower. According to Example 2 inWO 2013/048248 the desired benzene compound could be obtained in a yieldof 37%, whereas the yield on the desired benzene compound in US2010/0127220 amounted to about 41%. When the yields are calculated onthe basis of the starting furan compound the overall yield is about 30to 35% according to the examples in these documents.

It has now been found that the overall yield of the preparation processcan be increased when the dehydration step of the bicyclic unsaturatedether is preceded by a hydrogenation step, wherein the unsaturated bondof the bicyclic unsaturated ether that is obtained in the reaction ofthe furan compound with the olefin is hydrogenated. Surprisingly, thesaturated bicyclic ether thus obtained can still be dehydrated andaromatized, yielding the desired benzene compound.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for thepreparation of a benzene compound which comprises

(i) reacting a furan compound of formula (I):

wherein R¹ and R² are the same or different and independently selectedfrom the group consisting of hydrogen, alkyl, aralkyl, —CHO, —CH₂OR³,—CH(OR⁴)(OR⁵), —COOR⁶, wherein R³, R⁴ and R⁵ are the same or differentand are independently selected from the group consisting of hydrogen,alkyl, aryl, alkaryl, aralkyl, alkylcarbonyl and arylcarbonyl, orwherein R⁴ and R⁵ together form an alkylene group, and wherein R⁶ isselected from the group consisting of hydrogen, alkyl and aryl,with an olefin of the formula (II)

R⁷—CH═CH—R⁸  (II),

wherein R⁷ and R⁸ are the same or different and are independentlyselected from the group consisting of hydrogen, sulfonate, —CN, —CHO,and —COOR⁹, wherein R⁹ is selected from the group consisting ofhydrogen, and an alkyl group, or R⁷ and R⁸ together form a —C(O)—O—(O)C—group or a —C(O)—NR¹⁰—C(O)— group, wherein R¹⁰ represents hydrogen, analiphatic or an aromatic group,to produce an unsaturated bicyclic ether having an unsaturatedcarbon-carbon bond;(ii) hydrogenating the unsaturated carbon-carbon bond in the unsaturatedbicyclic ether to produce a saturated bicyclic ether; and(iii) dehydrating and aromatizing the saturated bicyclic ether toproduce the benzene compound.

DETAILED DESCRIPTION OF THE INVENTION

The first step of forming the unsaturated bicyclic ether from the furancompound of formula (I) and the olefin of formula (II) seems to occurvia a Diels-Alder-type reaction. It is known that Diels-Alder reactionsmay be reversible. Then the so-called retro-Diels-Alder reaction takesplace. Without wishing to be bound by any theory, it is believed that bythe hydrogenation of the double bond in the Diels-Alder adduct, i.e. theunsaturated bicyclic ether, the occurrence of the retro-Diels-Alderreaction is prevented. It is further surprising that in spite of thesaturation that is introduced into the bicyclic ether, the dehydrationand aromatization of the saturated ether does occur in satisfactoryyields.

It is known that in Diels-Alder reactions the reaction rate is expeditedby providing electron withdrawing groups on the olefin, i.e. thedienophile, and electron donating groups on the furan compound, i.e. thediene. Electron withdrawing groups include cyano, sulfonate, carboxylicacid, carboxylic anhydride, carboxylic ester, ketone and aldehydegroups. Electron donating groups include hydroxy, ether, aliphatic andaromatic hydrocarbon groups. Accordingly, the present inventionpreferably employs a furan compound of formula (I), wherein R¹ and R²are the same or different and independently selected from the groupconsisting of hydrogen, alkyl, aralkyl, —CHO, —CH₂OR³, wherein R³ isselected from the group consisting of hydrogen and alkyl. Morepreferably, R¹, R² and R³ are independently selected from the groupconsisting of hydrogen and an alkyl group having 1 to 4 carbon atoms.

The olefin of formula (II) suitably comprises compounds, wherein R⁷ andR⁸ are the same or different and are independently selected from thegroup consisting of hydrogen, —CHO and —COOR⁹, wherein R⁹ is selectedfrom the group consisting of hydrogen, and an alkyl group having 1 to 4carbon atoms, or R⁷ and R⁸ together form a —C(O)—O—(O)C— group. Morepreferably, R⁷ and R⁸ together form a —C(O)—O—(O)C— group. R⁷ and R⁸together may also form a —C(O)—NR¹⁰—C(O)— group, wherein R¹⁰ representshydrogen, an aliphatic or an aromatic group. When R¹⁰ is an aromatic oraliphatic group it may be optionally substituted. Suitable substituentsinclude hydroxyl, alkoxy, carbonyl, amino and hydrocarbonaceous groups.R¹⁰ may suitably be selected from alkyl and aromatic groups. The alkylgroup has typically from 1 to 15 carbon atoms, preferably from 1 to 6carbon atoms. R¹⁰ is suitably an aromatic group, which may be aheterocyclic aromatic moiety or a hydrocarbonaceous aromatic moiety. R¹⁰is preferably a hydrocarbonaceous aromatic moiety with 6 to 10 carbonatoms, more preferably a phenyl group.

The Diels-Alder reaction of the furan derivative of formula (I) with theolefin of formula (11) can be carried out at a broad variety of reactionconditions. Although elevated pressures may be applied, e.g., from 1 to100 bar, more preferably, from 1 to 10 bar, it is most feasible toconduct the reaction at autogenous pressure. The reaction temperaturemay also vary from far below 0° C. to elevated temperatures. Suitably,the reaction temperature varies from 0° C. to 150° C., preferably from20° C. to 100° C.

Known Diels-Alder catalysts may be used in the reaction. Suitablecatalysts include Lewis acids, e.g., aluminium, boron, zinc, hafnium,lithium or iron compounds, such as AlCl₃, Al(Et)Cl₂, Al(Et)₂Cl, BF₃,B(Ac)₃, ZnCl₂, ZnBr₂, Zn(Ac)₂, HfCl₄, FeCl₃, Fe(Ac)₃, FeCl₂ and Fe(Ac)₂,Zn(OTf)₂ (zinc triflate), LiOTf, Li (bisoxalato)borate, but also halidesof tin or titanium, such as SnCl₄ and TiCl₄. When a catalyst is used,the amount thereof may vary within wide ranges, such as from 0.01 to 50%mol, based on the furan compound of formula (I) or the olefin of formula(II), whichever is present in the lowest molar amount. Preferably, theamount of Diels-Alder catalyst is in the range of 0.1 to 20% mol, morepreferably from 0.2 to 15% mol, based on the amount of the furancompound of formula (I) or the olefin of formula (II), whichever ispresent in the lowest molar amount. However, dependent on the electrondonating behavior of the substituents on the furan compound and theelectron withdrawing nature of the substituents on the olefin, thereactants may be so reactive that a catalyst is not needed to make thereaction occur. Evidently, in such a case the skilled person may decidenot to use a catalyst in view of economic considerations.

Although it is possible to conduct the present reaction between thefuran derivative and the olefin in the presence of a solvent, it ispreferred to refrain from employing a solvent. Nevertheless, in certaincases the use thereof may be convenient. The use of a solvent isconvenient if the furan derivative and/or the unsaturated bicylic etherthat is being produced is solid under the reaction conditions. Theliquid phase thus obtained makes it easier to handle the reactant and/orthe reaction products. Thereto, the solvent may be selected from a widerange of potential liquids. Suitably, the solvent is selected from thegroup consisting of water, alcohols, esters, ketones, amides, aldehydes,ethers, ionic liquids and sulphoxides.

Advantageously, the solvents contain from 1 to 20 carbon atoms. Examplesof suitable alcohols include C₁-C₄ alcohols, in particular methanol,ethanol, n-propanol, isopropanol, butanol-1, butanol-2, 2-methylpropanoland tert-butanol. Suitable esters include the C₁-C₁₀ alkyl esters ofC₁-C₈ carboxylic acids, such as methyl formate, methyl acetate, ethylformate, ethyl acetate, methyl propionate, ethyl propionate, methylbutyrate, ethyl butyrate and ethylhexyl acetate. Suitable ketonescontain 2 to 8 carbon atoms, such as acetone, butanone and methyliso-butyl ketone. Suitable amides include acetamide and formamide,optionally substituted by one or two alkyl groups with 1 to 6 carbonatoms, such as N,N-dimethyl acetamide. Examples of suitable ethersinclude dialkyl ethers wherein each alkyl moiety is selected from aC₁-C₆ alkyl group, such as dimethyl ether, diethyl ether and methyltert-butyl ether, and also cyclic ethers such as tetrahydrofuran ordioxane. Suitable aldehydes include C₁-C₆ aldehydes, such asformaldehyde, acetaldehyde, propanal and hexanal. Suitable ionic liquidscomprise a pyridinium or imidazolinium moiety. Examples includepyridinium chloride, 1-ethyl-3-methylimidazolium dicyanamide and1-butyl-3,5-dimethylpyridinium bromide. A suitable sulphoxide isdimethylsulphoxide.

The relative amounts of the furan derivative of formula (I) and theolefin of formula (II) may vary. Since stoichiometry shows that one moleof furan may react with one mole of olefin, the molar ratio of theamount furan derivative to the amount of olefin generally will be about1:1, although the person skilled in the art may decide to provide one ofthe reactants in excess to promote the reaction and/or to facilitate thecomplete conversion of the other reactant. Therefore, the molar ratiobetween the amount of furan derivative to the amount of olefin suitablyranges from 0.1:1 to 10:1, preferably from 0.5:1 to 2:1, most preferablyabout 1:1.

For the Diels-Alder reaction, the reactants may be added in a batch-wiseor a continuous fashion. In a batch-wise fashion both the furanderivative and olefin are charged to a vessel, e.g. an autoclave, andmade to react with each other. Typically one of the reactants may beadded in portions, over a period of time, to the other reactant, e.g. byusing a syringe as described in US 2010/0127220. If desired, thereaction mixture is maintained at a desired temperature for a period oftime, e.g. whilst stirring to increase the yield of product. In acontinuous fashion both a stream of furan derivative and a stream ofolefin are fed to a reactor where they are contacted and from whichreactor continuously a stream of product is withdrawn. The flow rate ina continuous reactor should be adapted such that the residence time issufficient to allow a satisfactory conversion of the furan derivativeand olefin. The Diels-Alder reaction is suitably carried out in a batchor continuous reactor wherein the residence time is from 0.1 to 72hours, preferably from 0.5 to 48 hours.

When the process is conducted in a continuous mode, the reactor may beselected from various types of reactors, e.g. a continuous stirred tankreactor, a plug flow reactor or a trickle bed reactor when a solidcatalyst is used.

The unsaturated bicyclic ether thus obtained is subsequentlyhydrogenated. Thereto the unsaturated bicyclic ether is suitablycontacted with a reducing agent. Possible reducing agents includehydrides, such as LiH, NaH, NaAlH₄, LiAlH₄, NaBH₄ and CaH₂. However, theuse of gaseous hydrogen is preferred. When hydrogen gas is used ashydrogenation agent the use of a hydrogenation catalyst is desired.Accordingly, the present invention preferably is conducted in a processwherein the unsaturated carbon-carbon bond in the unsaturated bicyclicether is hydrogenated using gaseous hydrogen in the presence of ahydrogenation catalyst. Suitable hydrogenation catalysts comprise one ormore metals or metal compounds selected from the metals in the Groups 8to 10 of the Periodic Table of Elements, preferably on a carrier. Suchsuitable metals include Pt, Pd, Ru, Rh, Ir, Os, Ni, Co and mixturesthereof.

The carriers for these metals may be selected from a variety ofconventional carriers. Preferably, the carrier has been selected fromalumina, silica, titania, zirconia, silica-alumina, carbon, morepreferably activated carbon, and mixtures thereof. The loading of themetal or metals on the carrier may also be varied within wide ranges.The content of metal on the hydrogenation catalyst may be in the rangeof 0.5 to 25% wt, more suitably from 1 to 10% wt, based on the weight ofthe hydrogenation catalyst.

Although the hydrogenation catalyst may be selected from any combinationof the metals and carriers that are described herein, the most preferredhydrogenation catalyst is selected from palladium, platinum or rutheniumon activated carbon, in particular palladium on activated carbon.

It may be convenient to hydrogenate the unsaturated carbon-carbon bondin the unsaturated bicyclic ether in the presence of a solvent. The useof a solvent may render it easier to handle and to disperse thehydrogenation catalyst uniformly in the mixture of unsaturated bicyclicether, gaseous hydrogen and solvent. The solvent may also facilitate theuptake of hydrogen, which promotes the hydrogenation reaction. When asolvent is used the solvent can suitably be selected from the groupconsisting of hydrocarbons, alcohols, esters, ketones, amides,aldehydes, ethers, ionic liquids and sulphoxides. It is advantageous touse a solvent that is not subjected to possible hydrogenation itself.Therefore, the use of saturated hydrocarbons or ethers is more suitable.Such suitable solvents, therefore, include C₄-C₁₀ aliphatic hydrocarbonsor mixtures thereof and saturated ethers such as dialkyl ethers, whereineach alkyl moiety is selected from a C₁-C₆ alkyl group, or mixturesthereof, or cyclic ethers such as dioxane and tetrahydrofuran. Goodresults have been obtained by using a solvent that has been selectedfrom the group consisting of saturated hydrocarbons and ethers, inparticular cyclic ethers.

The hydrogenation conditions may vary within wide ranges. The skilledperson will realize that the conditions may also be varied in accordancewith the nature of the substituents. In order to selectively hydrogenatethe unsaturated carbon-carbon bond in the unsaturated bicyclic ether,the hydrogenation temperature is kept at a moderate level. Lowtemperatures were found to reduce the retro Diels-Alder reactions.Suitably, the unsaturated bicyclic ether is hydrogenated at atemperature of 0 to 150° C., preferably from 10 to 100° C., morepreferably from 20 to 80° C.

The hydrogen pressure may also be selected within a broad range. Theunsaturated bicyclic ether is suitably hydrogenated at a hydrogenpressure of 1 to 125 bar, preferably at a hydrogen pressure of 10 to 100bar. The reaction is completed when no hydrogen is taken up anymore. Theduration of the hydrogenation reaction may typically be in the range of0.5 to 24 hrs, suitably from 2 to 16 hrs.

Surprisingly the hydrogenation reaction can be substantiallyquantitative. Thus the saturated bicyclic ether is obtained in excellentyield and purity. If desired, the hydrogenated saturated bicyclic ethermay be purified. This may be accomplished by washing the saturatedbicyclic ether and/or by recrystallization from a suitable solvent. Suchsolvents can be selected from alcohols, hydrocarbons, esters, ethers andmixtures thereof.

The saturated bicyclic ether is then subjected to dehydration andaromatization. Since in the dehydration also hydrogen is liberated, theprocess according to the present invention does not require net hydrogenaddition.

According to WO 2013/048248 the dehydration of the unsaturated bicyclicether can be accomplished in the presence of a catalyst. The catalystmay be acidic or alkaline. A preference is expressed for an alkalinecatalyst, such as an alcoholate, hydroxide, carboxylate or carbonate.Also in the process according to the present invention the saturatedbicyclic ether is suitably dehydrated and aromatized in the presence ofa catalyst. Different from the preference in WO 2013/048248, it has nowsurprisingly been found that the dehydration and aromatization of thesaturated bicyclic ether is suitably performed in the presence of anacid catalyst. The acid catalyst can be a homogeneous or a heterogeneouscatalyst. The use of a homogeneous catalyst boils down to a processwherein the reaction is carried out in a homogeneous liquid phase andthe catalyst is comprised in that liquid phase. Suitable homogeneouscatalysts that may be dissolved in the appropriate solvent to yield ahomogeneous catalytic environment include organic and inorganic acids,such as alkane carboxylic acid, arene carboxylic acid, alkane sulphonicacid, such as methane sulphonic acid, arene sulphonic acid, such asp-toluene sulphonic acid, sulphuric acid, phosphoric acid, hydrochloricacid, hydrobromic acid and nitric acid. When an arene carboxylic acid isthe eventually desired product, such as phthalic acid, methylphthalicacid, isophthalic acid or hemimellitic acid, a preferred arenecarboxylic acid is selected from phthalic acid, methylphthalic acid,isophthalic acid and hemimellitic acid, since these acids providescatalytic activity and do not add an extraneous chemical to the reactionmixture.

Preferably, the dehydration and aromatization is carried out in thepresence of a heterogeneous catalyst. When a heterogeneous catalyst isused, the reaction is conducted in a liquid reactant phase and a solidcatalyst phase. Hence, the catalyst is preferably a solid catalyst.Examples of solid acidic catalysts include amorphous silica-alumina,zeolites, preferably zeolites in their H-form, phosphoric acid on acarrier, sulfonated activated carbon and acidic ion exchange resins,wherein zeolites, ion exchangers, sulfonated activated carbon andcombinations thereof are preferred. Zeolites are particularly preferred.Zeolites are the preferred catalysts since they can withstand relativelyhigh reaction temperatures and their acidity can be adjusted byselecting the desired level of ion exchange of metal ions by protonsand/or by varying the silica-alumina ratio in the zeolite. The zeolitecan be selected from a variety of zeolitic structures. In principle allzeolitic structures as defined in the Database of Zeolite Structures andapproved by the Structure Committee of the International ZeoliteAssociation can be used. Good results have been obtained with thezeolites selected from the group consisting of zeolite Y, zeolite X,zeolite beta, mordenite and mixtures thereof. Zeolites are crystallinealuminosilicates that contain certain alkali and alkaline earth cations,such as sodium or magnesium ions. By varying the silica/alumina ratioand by varying the removal of the alkali and alkaline earth metalcations and replacing them by protons, the acidity of the zeolite can beadjusted. Typically, the zeolite has a silica/alumina molar ratio in therange of 1 to 200. Suitably the zeolite has been subjected to ionexchange to remove alkaline and alkaline earth cations and have thesecations replaced by protons. An alternative preferred solid acidiccatalyst is sulfonated activated carbon. This catalyst comprisessulfonic acid groups attached to activated carbon. The preparationthereof has e.g. been described in Liu et al, Molecules, 2010, 15,7188-7196.

The skilled person will realize that the amount of acidic catalyst canbe varied within broad ranges. It has been found that it is advantageousto use the acidic catalyst in an amount in the range of 10% wt to 50%wt, based on the amount of substrate, i.e. the saturated bicyclic ether.When smaller amounts of catalyst are used the reaction may take longer.

It is advantageous to dehydrate and aromatize the saturated bicyclicether neat. This promotes the contact of the saturated bicyclic etherwith the catalyst. In other embodiments it is desirable to conduct thedehydration and aromatization in the presence of a solvent. Thedispersion of the solid catalyst is then facilitated. If a solvent isused, the nature of the solvent is not critical, and the solvent cansuitably be selected from the group consisting of aliphatic and aromatichydrocarbons, alcohols, esters, ketones, amides, aldehydes, ethers,ionic liquids and sulphoxides, preferably hydrocarbons, more preferably,aromatic hydrocarbons. The use of aromatic hydrocarbon solvents ispreferred since the solubility of the eventual benzene compound tends tobe high in the aromatic hydrocarbon solvent. Preferably, the aromatichydrocarbon solvent is toluene, xylene or a mixture thereof.

In the dehydration and aromatization reaction not only water is splitoff from the saturated bicyclic ether, but also one molecule of hydrogenper molecule of saturated bicyclic ether is removed during thedehydration and aromatization. It has therefore been considered toemploy a dehydrogenation catalyst, in addition to an acidic catalystthat promotes the dehydration. Dehydrogenation catalysts include metaloxides as well as metals, usually on a carrier. Suitable catalystsinclude chromia and iron oxide as examples of a metal oxide catalyst,and noble metals, such as Pt, Pd, Ru and Rh, on activated carbon assupported metal catalyst.

Although the use of such catalysts allow for more modest reactionconditions, such as a relatively low temperature, it has been found thatthe catalyst also promotes the formation of saturated by-products.Without wishing to be bound by any theory, it is believed that hydrogenthat is split off from the saturated bicyclic ether to form a benzenecompound, is subsequently used to hydrogenate another molecule to form acyclohexene compound. This reaction is believed to be promoted by adehydrogenation catalyst.

When the dehydration and aromatization is carried out in the absence ofa solvent, the dehydration and aromatization step is preferablyconducted in the presence of a solid acidic catalyst and in the absenceof a dehydrogenation catalyst. When a solvent is present in thedehydration and aromatization step, it is suitable to include also adehydrogenation catalyst.

The dehydration and aromatization occurs at a reaction temperature thatis preferably in the range of 100 to 350° C., preferably from 125 to275° C. When also a dehydrogenation catalyst and a solvent are presentin the reaction mixture, the temperature is suitably somewhat lower,such as from 75 to 250° C., preferably from 100 to 200° C. Theatmosphere is typically inert; the reaction is suitably carried outunder nitrogen, helium, neon or argon. The pressure in the dehydrationand aromatization step is preferably ranging from 0.5 to 50 bar. Thesaturated bicyclic ether is suitably dehydrated and aromatized in abatch or continuous reactor wherein the residence time is from 0.1 to 48hours.

The present process is excellently suited for the preparation ofaromatic acids, such as methylphthalic acid or anhydride andhemimellitic acid. It is also possible to prepare other benzenecompounds, such as benzene, toluene, xylene, benzoic acid, toluic acid,and similar compounds, in this way. Via this route the provision ofthese acids or these other benzene compounds from a sustainable sourcehas become available. The furan compound of formula (I) can be preparedfrom the conversion of carbohydrates, as explained in WO 2013/048248 andWO 2007/104514. Therefore, the present invention also provides thepreparation of a substituted benzene compound wherein the benzenecompound produced by the dehydration and aromatization of the saturatedbicyclic ether is oxidized. In this way the substituents on the benzenecompound that contain a carbon atom are converted into carboxylic acidgroups.

The oxidation may be conducted in a known manner. Thereto, the oxidationis suitably accomplished by an oxygen-containing gas in the presence ofa catalyst comprising cobalt and manganese or by alkali metalpermanganate, such as potassium permanganate, or nitric acid. Aromaticcarboxylic acids may suitably be prepared over a catalyst that containsbromine in addition to cobalt and manganese. Preparation of such acatalyst has, for instance, been described U.S. Pat. No. 4,138,354. Theoxygen-containing gas may be air, oxygen-enriched air or substantiallypure oxygen. When the benzene compound contains an oxygen atom in itssubstituents, other, more conventional and/or less expensive catalystsare also possible since such benzene compounds are more reactive andeasier to oxidize than benzene compounds that do not have an oxygen atomin their substituents. Therefore, oxidation using potassiumpermanganate, nitric acid, or using oxygen over noble metal-containingcatalyst (e.g., Rh, Pd) is also possible.

The temperature and pressure of the oxidation can be selected withinwide ranges. The pressure of the reaction mixture is preferably between1 and 100 bar, with a preference for pressures between 10 and 80 bar. Incase the oxidant is an oxygen-containing gas, such as air, the gas canbe continuously fed to and removed from the reactor, or all of the gascan be supplied at the start of the reaction. In the latter case, thepressure of the system will depend on the headspace volume and theamount of gas required for converting the starting material. It is clearthat in the latter case, the pressure of the system may be significantlyhigher than when an oxygen-containing gas is continuously fed andremoved.

The temperature of the reaction mixture at the oxidation is suitablybetween 60 and 300° C., preferably between 100 and 260° C., morepreferably between 150 and 250° C., most preferably between 160 and 220°C.

In the preferred oxidation catalysts that comprise Co and Mn, molarratios of cobalt to manganese (Co/Mn) are typically 1/1000-100/1,preferably 1/100-10/1 and more preferably 1/10-4/1.

Likewise, in these preferred oxidation catalysts, comprising alsobromine, molar ratios of bromine to metals (i.e. Br/(Co+Mn)) aretypically from 0.001 to 5.00, preferably 0.01 to 2.00 and morepreferably 0.1 to 0.9.

Catalyst concentration (calculated on the metal, e.g., Co+Mn) ispreferably between 0.1 and 10 mol % relative to the starting material,with a preference for loads between 2 and 6 mol %. Good results will beobtained in general with catalyst loads of around 4 mol % relative tothe starting benzene compound.

Reaction times suitably range from 0.1 to 48 hours, preferably from 0.5to 24 hrs. The skilled person will realize that the number of carboxylicgroups on the benzene ring may be varied. He may vary this number byselecting the appropriate starting materials. Alternatively, he may wantto decarboxylate the products, using a method similar to the onedescribed in U.S. Pat. No. 2,729,674 for the mono-decarboxylation oftrimellitic acid. Such decarboxylation involves the application of arelatively high temperature, such as from 200 to 400° C. Sincedecarboxylation may occur at temperatures of about 200° C., somedecarboxylation may already occur when the aromatization of thesaturated bicyclic ether is carried out at temperatures of at least 200°C. and when the saturated bicyclic ether contains carboxylic groups assubstituents. In the process of the present invention decarboxylationmay be used to arrive at the desired benzene compound. By applyinglonger reaction times and/or higher reaction temperatures, the rate ofdecarboxylation can be influenced. It was also found that thedecarboxylation readily occurs at temperatures from 200° C. when thearomatization is carried out in the absence of a solvent. When a solventis present in the aromatization step, significantly higher temperaturesare required to accomplish significant decarboxylation. Another knowndecarboxylation process uses a diazabicyclo alkene at elevatedtemperatures as shown in U.S. Pat. No. 4,262,157.

The invention enables the provision of certain novel intermediatecompounds. Accordingly the present invention provides the hydrogenatedDiels-Alder adduct of the formula (III)

wherein X and Y are different and independently selected from the groupconsisting of hydrogen, alkyl, aralkyl, —CHO, —CH₂OR³, —CH(OR⁴)(OR⁵),—COOR⁶, wherein R³, R⁴ and R⁵ are the same or different and areindependently selected from the group consisting of hydrogen, alkyl,aryl, alkaryl, aralkyl, alkylcarbonyl and arylcarbonyl, or wherein R⁴and R⁵ together form an alkylene group, and wherein R⁶ is selected fromthe group consisting of hydrogen, alkyl and aryl; and wherein R⁷ and R⁸are the same or different and are independently selected from the groupconsisting of sulfonate, —CN, —CHO, and —COOR⁹, wherein R⁹ is selectedfrom the group consisting of hydrogen, and an alkyl group, or R⁷ and R⁸together form a —C(O)—O—(O)C— group or a —C(O)—NR¹⁰—C(O)— group, whereinR¹⁰ represents hydrogen, an aliphatic or an aromatic group. Thehydrogenated Diels-Alder adduct is an oxa-[2,2,1]-bicyclo-heptanecompound.

More in particular the invention provides a hydrogenated Diels-Alderadduct of formula (IV)

wherein X and Y are different and independently selected from the groupconsisting of hydrogen, —CHO, —CH₂OR³, —COOR⁴, wherein R³ is selectedfrom the group consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl,alkylcarbonyl and arylcarbonyl, and wherein R⁴ is selected from thegroup consisting of hydrogen, alkyl and aryl

It has further been found that the dehydration and aromatizationreaction of the saturated bicyclic ether yields a lactone. It isbelieved that this lactone is an intermediate product in the formationof the eventual benzene compound. This benzene compound can therefore beprepared by subjecting such a lactone to the same reaction conditions asthe desired for the formation of the benzene compound from the saturatedbicyclic ether. The present invention therefore also provides a lactonecompound of formula (V)

wherein Y is hydrogen and X is selected from the group consisting ofalkyl, aralkyl, —CHO, —CH₂OR³, —CH(OR⁴)(OR⁵), —COOR⁶, wherein R³, R⁴ andR⁵ are the same or different and are independently selected from thegroup consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl,alkylcarbonyl and arylcarbonyl, or wherein R⁴ and R⁵ together form analkylene group, and wherein R⁶ is selected from the group consisting ofhydrogen, alkyl and aryl.

More preferably, Y is hydrogen and X is selected from the groupconsisting of alkyl, aryl, alkaryl, aralkyl, —CHO, or —CH₂OR³, whereinR³ is selected from the group consisting of hydrogen, alkyl and aryl.The alkyl, aryl, aralkyl or alkaryl groups suitably have at most 10carbon atoms. The alkyl groups may preferably have from 1 to 4 carbonatoms.

The invention will be illustrated by means of the following examples.

Example 1 Diels-Alder Reaction of (Substituted) Furan and MaleicAnhydride

A round-bottom flask equipped with water-cooled condenser and mechanicalover-head stirrer was charged with a furan compound as indicated inTable 1 (1.2 mmol) and maleic anhydride (1.0 mmol). The suspension wasstirred at 15-20° C. using a water bath. During the course of thereaction, the mixture turned to a clear homogeneous liquid after areaction time as indicated in Table 1. Pale-yellow colored crystallinematerial crystallized from the liquid. The yield was as indicated inTable 1, relative to the molar amount of maleic anhydride. ¹H NMRspectroscopy further revealed the purities of the adducts, as shown inTable 1. Percentages are molar percentages, based on the number of molesof maleic anhydride.

The results and conditions are shown in Table 1.

TABLE 1 Exp. Reaction No. X Y time, hr Yield, % Purity, % 1 —H —H 3 9894 2 —CH₃ —H 4 >95 93 3 —CH₃ —CH₃ 3 96 94 4 —CH₂—O—CH₃ —H 18 >85 80 5—CH₂—O—C₂H₅ —H 26 >85 80

Example 2

Hydrogenation of Diels-Alder Adduct from Furan Compounds and MaleicAnhydride

A pressure reactor was charged with 100 parts by weight (pbw) of crudeadduct obtained in Example 1 (see Table 2), 2 pbw of catalyst Pd/C(containing 10% wt Pd, based on the catalyst), and THF in a quantity of5 mL per gram adduct. The reactor was purged 3 times with nitrogen of4-5 bar, and then pressurized with hydrogen to 80 bar. The reactionmixture was stirred at room temperature at 300 rpm. During the progressof the reaction the hydrogen pressure dropped, but the reactor wassubsequently re-pressurized to 80 bar. When the consumption of hydrogengas stopped, the reaction was completed. The reaction time is indicatedin Table 2. Excess hydrogen pressure was cautiously vented off and thereactor was flushed 3 times with nitrogen of 4-5 bar. The mixture wasfiltered yielding a pale yellow clear solution, which was evaporated todryness under reduced pressure using a rotary evaporator. The crudeproduct was further purified by recrystallization from methanol or ethylacetate which resulted in hydrogenated Diels-Alder adduct as colorlesssolid in a yield and with a purity, as determined by NMR and GC analysisand indicated in Table 2. Percentages are molar percentages, based onstarting material (yield) or on product.

TABLE 2 Exp. Reaction No. X Y time t, hrs Yield, % Purity, % 6 —H —H 3-5~100 96 7 —CH₃ —H 3-5 ~100 95 8 —CH₃ —CH₃ 3-5 ~100 98 9 —CH₂—O—CH₃ —H 589 90 10 —CH₂—O—C₂H₅ —H 5 85 89

Example 3 Diels-Alder Reaction of Substituted Furan and Methyl Acrylate

A round-bottom flask equipped with water-cooled condenser and mechanicalover-head stirrer was charged with a furan compound as indicated inTable 3 (1.2 mmol), methyl acrylate (1.0 mmol) and zinc iodide (0.3mmol). The suspension was stirred at 40° C. for 48 h. After thecompletion of reaction, the mixture was diluted with ethyl acetate andwashed with 0.1M aqueous solution of Na₂S₂O₃, dried and concentrated toafford pale-yellow colored liquid. The yield was as indicated in Table3.

TABLE 3 Reaction Time Exp. No. X Y (h) Yield (%) 11 CH₃ H 48 43 12 CH₃CH₃ 48 45

Example 4

Hydrogenation of Diels-Alder Adduct from Furan Compounds and MethylAcrylate

A pressure reactor was charged with 100 parts by weight (pbw) of crudeadduct obtained in Example 3 (see Table 4), 2 pbw of catalyst Pd/C(containing 10% wt Pd, based on the catalyst), and THF in a quantity of5 mL per gram adduct. The reactor was purged 3 times with nitrogen of4-5 bar, and then pressurized with hydrogen to 80 bar. The reactionmixture was stirred at room temperature at 300 rpm. During the progressof the reaction the hydrogen pressure dropped, but the reactor wassubsequently re-pressurized to 80 bar. When the consumption of hydrogengas stopped, the reaction was completed. The reaction time is indicatedin Table 4. Excess hydrogen pressure was cautiously vented off and thereactor was flushed 3 times with nitrogen of 4-5 bar. The mixture wasfiltered yielding a pale yellow clear solution, which was evaporated todryness under reduced pressure using a rotary evaporator. The crudeproduct was further purified by a short filtration through silica gelaffording hydrogenated Diels-Alder adduct, an oxa-bicyloheptane compoundwith a methylcarboxylate substituent on the 2- or 3-position, aspale-yellow coloured liquid.

TABLE 4 Reaction Time Exp. No. X Y (h) Yield (%) 13 CH₃ H 12 90 14 CH₃CH₃ 12 92

Example 5 Aromatization of Hydrogenated Diels-Alder Adduct Over Acid andDehydrogenation Catalysts

A stainless steel pressure reactor was charged with the productsobtained in experiments 7 and 8 of Example 2 (see Table 2) (1.0 mmol),an acid zeolite Y catalyst in an amount of 50 pbw per 100 pbw of theproduct of experiments 7 and 8 of Example 2, respectively, 3 pbw of Pd/C(10 wt % of Pd based on the weight of the catalyst) and toluene (20 mL/gproduct). Next, the reactor was purged 3 times with nitrogen of 10 bar,and the reaction mixture was stirred (750 rpm) at 150-200° C. for 24 h.During the course of reaction, the pressure rose to a maximum of 6-8bar. After completion of the reaction, the reactor was cooled down toroom temperature and the excess pressure was carefully vented off. Thecrude reaction mixture was filtered using a filter aid and washed 5times with 10 mL toluene, giving a pale yellow clear solution, which wasthen evaporated to dryness under reduced pressure using a rotaryevaporator to give yellow colored crystalline material. The analysis ofcrude product using ¹H NMR spectroscopy confirmed the formation ofdesired aromatic compound, viz. optionally substituted phthalicanhydride together with up to four different by-products (based on thecatalyst used). The products distribution was calculated by NMRanalyses, using 1,4-dinitrobenzene as internal standard.

The yields of the respective products are shown in Table 5. Percentagesare molar percentages, based on starting material.

TABLE 5 Exp. Acid Dehydrog. Yield of Product, % No. X Y catalystCatalyst 1 2 3 4&5 6 15 —CH₃ —CH₃ H—Y Pd/C 67 — — 12* — 16 CH₃ —H H—YPd/C 59 0 0 21 —+ *in this case, it is para-xylene. + any toluene formedwas not detectable as the reaction was performed in toluene as solvent

Example 6 Aromatization of Hydrogenated Diels-Alder Adduct Over AcidCatalyst

In experiment Nos. 17 and 18 a round-bottom flask was charged with eachof the products obtained in Example 4 (1.0 mmol) and solid acid catalyst(100 pbw per 100 pbw of product). The acid catalyst was selected from anacid zeolite Y with a silica-alumina ratio of 5.2 (“H—Y”). Next, theflask was purged 3 times with nitrogen and inserted into a glass oven at200° C. The reaction flask was rotated at 25 rpm for about 2.0 hr undernitrogen atmosphere. After completion of the reaction, the glass ovenwas cooled down to room temperature. The crude reaction mixture wasdissolved in chloroform (CDCl₃) and filtered and washed 3 times with 10mL CDCl₃, giving a pale yellow clear solution, which was then evaporatedto dryness under reduced pressure using a rotary evaporator. A yellowcolored crystalline material was thus obtained. The analysis of crudeproduct using ¹H NMR spectroscopy confirmed the formation of desiredbenzene compound, i.e. the benzene compound with a carboxylate moiety onthe 2- or 3-position, and the calculated product yield about was 20-30%molar.

Example 7 Solvent-Free Aromatization of Hydrogenated Diels Alder AdductOver Acid Catalyst

A round-bottom flask was charged with a product obtained in Example 2(1.0 mmol) and solid acid catalyst (100 pbw per 100 pbw of product). Theacid catalyst was selected from an acid zeolite Y with a silica-aluminaratio of 5.2 (“H—Y”), such zeolite Y catalyst that contained 1% wt Pd(“Pd/H—Y”), such zeolite Y catalyst that contained 0.25% wt Pt and 0.25%wt Pd (“Pt/Pd/H—Y”). Next, the flask was purged 3 times with nitrogenand inserted into a glass oven at 200° C. The reaction flask was rotatedat 25 rpm for about 2 to 3 hr under nitrogen atmosphere. Aftercompletion of the reaction, the glass oven was cooled down to roomtemperature. The crude reaction mixture was dissolved in chloroform(CDCl₃) and filtered and washed 3 times with 10 mL CDCl₃, giving a paleyellow clear solution, which was then evaporated to dryness underreduced pressure using a rotary evaporator. A yellow colored crystallinematerial was thus obtained. The analysis of crude product using ¹H NMRspectroscopy confirmed the formation of desired aromatic compound, viz.optionally substituted phthalic anhydride together with up to threedifferent by-products (dependent on the catalyst used). The productdistribution in the crude mixture was calculated by NMR analyses using1,4-dinitrobenzene as internal standard.

The compounds, the catalyst used, and the yields of the respectiveproducts are shown in Table 7. Percentages are molar percentages, basedon starting material.

TABLE 7 Exp. Acid Yield of Product, % No. X Y catalyst 1 2 3&4 5 19 —H—H H—Y 41 — 26 23 20 —CH₃ —H H—Y 76 — 13 — 21 —CH₃ —CH₃ H—Y 72 — 11 1722 —CH₃ —H Pd/H—Y 80 —  7 —* 23 —CH₃ —H Pt/Pd/H—Y 62 — 17 —***Experiment 22 also yielded 5% of 3-methyl-1,2-dicarboxylicanhydride-cyclohexene-1. **Experiment 23 also yielded 10% of3-methyl-1,2-dicarboxylic anhydride-cyclohexene-1.

Example 8 Effect of Time and Temperature on the Aromatization ofSaturated Bicyclic Ether Over Acid Catalyst

A round-bottom flask was charged with a product obtained in Example 2(1.0 mmol) and solid acid catalyst (50 pbw or 100 pbw per 100 pbw ofproduct). The acid catalysts used were the same as those used in Example7. Next, the flask was purged 3 times with nitrogen and inserted into aglass oven at a fixed temperature. The reaction flask was rotated at 25rpm for a fixed amount of time under nitrogen atmosphere. Subsequently,the glass oven was cooled down to room temperature. The crude reactionmixture was dissolved in chloroform (CDCl₃) and filtered and washed 3times with 10 mL CDCl₃, giving a pale yellow clear solution, which wasthen evaporated to dryness under reduced pressure using a rotaryevaporator. A yellow colored crystalline material was thus obtained. Theanalysis of crude product using ¹H NMR spectroscopy confirmed theformation of desired aromatic compound, viz. optionally substitutedphthalic anhydride together with up to three different by-products(dependent on the catalyst used). The product distribution in the crudemixture was calculated by NMR analyses using 1,4-dinitrobenzene asinternal standard.

The compounds, the catalyst used, and the yields of the respectiveproducts are shown in Table 8. Percentages are molar percentages, basedon starting material.

TABLE 8 Exp. Temp. Time Conv. Yield of Product, % No. X Y (° C.) (hrs)Acid catalyst (%) 1 2 3&4 5 24 —CH₃ —H 150  2 H—Y (50%)  89 12 77  0  025 —CH₃ —H 150 15 H—Y (50%) 100 34 66  0  0 26 —CH₃ —H 160  2 H—Y (50%)100 24 76  0  0 27 —CH₃ —H 175  2 H—Y (50%) 100 37 63  0  0 28 —CH₃ —H160  2 H—Y (100%) 100 43 54  0  0 29 —CH₃ —H 175  2 H—Y (100%) 100 81  9 6  0 30 —CH₃ —H 200  2 H—Y (100%) 100 76  0  6  13 31 —CH₃ —H 225  2H—Y (100%) 100 45  0  0  55 32 —CH₃ —H 250  5 H—Y (100%) 100  0  0  0100 33 —H —H 160 15 H—Y (100%)  43 15 28  0  0 34 —H —H 200  2 H—Y(100%) 100 41  0 26  23 35 —CH₃ —CH₃ 200  2 H—Y (100%) 100 72  0 11  17

1.-34. (canceled)
 35. A hydrogenated Diels-Alder adduct of the formula(III)

wherein X and Y are different and independently selected from the groupconsisting of hydrogen, alkyl, aralkyl, —CHO, —CH₂OR³, —CH(OR⁴)(OR⁵),—COOR⁶, wherein R³, R⁴ and R⁵ are the same or different and areindependently selected from the group consisting of hydrogen, alkyl,aryl, alkaryl, aralkyl, alkylcarbonyl and arylcarbonyl, or wherein R⁴and R⁵ together form an alkylene group, and wherein R⁶ is selected fromthe group consisting of hydrogen, alkyl and aryl; and wherein R⁷ and R⁸are the same or different and are independently selected from the groupconsisting of sulfonate, —CN, —CHO, and —COOR⁹, wherein R⁹ is selectedfrom the group consisting of hydrogen, and an alkyl group, or R⁷ and R⁸together form a —C(O)—O—(O)C— group or a —C(O)—NR¹⁰—C(O)— group, whereinR¹⁰ represents hydrogen, an aliphatic or an aromatic group.
 36. Ahydrogenated Diels-Alder adduct of the formula (IV)

wherein X and Y are different and independently selected from the groupconsisting of hydrogen, —CHO, —CH₂OR³, —COOR⁴, wherein R³ is selectedfrom the group consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl,alkylcarbonyl and arylcarbonyl, and wherein R⁴ is selected from thegroup consisting of hydrogen, alkyl and aryl.
 37. A lactone compound offormula (V)

wherein Y is hydrogen and X is selected from the group consisting ofalkyl, aralkyl, —CHO, —CH₂OR³, —CH(OR⁴)(OR⁵), —COOR⁶, wherein R³, R⁴ andR⁵ are the same or different and are independently selected from thegroup consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl,alkylcarbonyl and arylcarbonyl, or wherein R⁴ and R⁵ together form analkylene group, and wherein R⁶ is selected from the group consisting ofhydrogen, alkyl and aryl.
 38. The lactone compound according to claim37, wherein Y is hydrogen and X is selected from the group consisting ofalkyl, aralkyl, —CHO, or —CH₂OR³, wherein R³ is selected from the groupconsisting of hydrogen, alkyl and aryl.